In conventional key telephone apparatuses whereto such hybrid terminal devices can be connected (hereafter referred to as hybrid key telephone apparatuses), an interface circuit for two-wire digital terminal device and an interface circuit for two-wire analog terminal device are connected to an analog terminal device or a digital terminal device by means of switching using a switch or by replacing the interface circuit itself.
FIG. 2 is a configuration diagram of a conventional key telephone apparatus having so-called hybrid terminal devices, i.e., a conventional key telephone apparatus whereto an analog terminal device and a digital terminal device are simultaneously connected by means of switching using a switch. FIG. 3 is a configuration diagram of a conventional key telephone apparatus having a so-called hybrid terminal device, i.e., a conventional key telephone apparatus whereto an analog terminal device and a digital terminal device are simultaneously connected by means of individual interface circuits.
In FIG. 2, numeral 1 denotes a main device of a key telephone apparatus. This main device 1 has both an interface circuit 2 for analog terminal device and an interface circuit 3 for digital terminal device. Numeral 4 denotes an analog terminal device connected to the interface circuit 2 for analog terminal device via a port a, and numeral 5 denotes a digital terminal device connected to the interface circuit 3 for digital terminal device via a port c. A port b is a so-called hybrid port which is connected to the interface circuit 2 for analog terminal device (as illustrated) by means of switching in an interacting switch 7 when a terminal device 8 is an analog terminal device and which is connected to the interface circuit 3 for digital terminal device when the terminal device 8 is a digital terminal device.
On the other hand, FIG. 3 shows a hybrid key telephone apparatus whereto the above described analog terminal device 4 and digital terminal device 5 can be connected. In this apparatus, ports d and e are so fixed as to be analog terminal device connection port and digital terminal device connection port, respectively. When a terminal device must be replaced, therefore, the interface circuit 2 for analog terminal device or the interface circuit 3 for digital terminal device may be replaced.
Once setting in the main device 1 is performed in a conventional hybrid key telephone apparatus having the above described configuration shown in FIG. 2 or FIG. 3 according to the terminal device to be connected, however, the port whereto the terminal device is connected is so fixed as to be used for either analog terminal device or digital terminal device, and hence it is extremely difficult for the user to change the setting, resulting in a problem.